Wires and cables used for conducting electricity are made of conducting metal with a wide variety of diameters and cross-sectional profiles. The wire may be surrounded by one or more layers of nonconducting material as insulation, and the insulation may again be surrounded by a shield of woven or solid metal. This again may be surrounded by a protective coating of rubber or polymers. Such an assembly of layers around multiple strands of wire is usually called a cable.
A specialized kind of wire conductor is used as the heating element in kitchen ranges and ovens. A metal conductor, usually made of a higher-resistivity alloy with a high melting point, is enclosed in a hollow tube of a high-temperature and corrosion-resistant alloy. The space between wire and tube is filled with a powdered fire-resistant material such as magnesium oxide which at all temperatures of use is a non-conductor of electricity. Such assembly is sealed at the ends and then drawn through a die of a desired size and configuration, causing the tube and its contents to become thinner and longer. The drawing action is repeated until the tube has been reduced to the desired diameter and cross-sectional profile. The result is a stiff "shielded" wire where the central conducting wire is embedded in a highly compacted insulator and the whole assembly is protected by an external metal shell. Pieces of this wire can be cut and bent into a desired shape. At the ends the conducting core can be connected to current-carrying contacts in order to complete an electric circuit.
It has long been known that at sufficiently low temperatures certain materials become superconductors of electric currents by virtue of extremely low (or absence of) electrical resistance. Much research work is being directed to finding materials which will be superconducting at temperatures above the atmospheric boiling point of liquid nitrogen. So far, these materials have been found to be ceramic type materials. A ceramic is a composition of metallic elements and oxygen which is hard and brittle. Such materials are more fully described in the following publications:
(1) Maeda et al., Jap. J. Appl. Phys. 27, L209-L210 (1988), describing the Bi.sub.2 -Sr-Ca-Cu system; PA0 (2) Subramanian et al., Science, 239,1015-1017 (1988), describing the crystal structure of the above system; PA0 (3) Subramanian et al., Nature, 332, 420-422 (1988) describing the structure of a T1-system.
In transmitting electrical energy, a superconductor would be most useful in the form of a wire or cable. However, due to the hard and brittle nature of ceramic materials, the ceramic superconductors do not naturally lend themselves easily to such applications. This is confirmed by a new note entitled "Researchers Produce Large-Current Superconductor Wire" in the July, 1988 issue of Research & Development wherein superconducting fibers are reported to have been pulled from a melt. Such fibers are said to require a temperature of 4.degree. K. and are quite small as indicated by the current capacity of 30,000 A/cm.sup.2.
Accordingly, it is an object of the present invention to provide a means whereby superconductor materials can be formed into a wire or cable. It is a further object of this invention to provide a means for protecting the superconducting wire from damage when the superconducting property is interrupted or lost.